The present invention relates to a semiconductor device constituting a DC/DC converter installed in a portable electronic instrument or the like, and more particularly to a small, thin semiconductor device with an inductor formed by laminating together a semiconductor chip forming an integrated circuit and a thin inductor.
A distribution type power supply IC used in a portable electronic instrument such as a portable telephone, digital camera, or digital video camera, or an individual power supply IC that compensates for deficiencies in a centralized power supply, is structured such that a power supply IC chip forming an integrated circuit of an output portion and a control portion is die-bonded to a lead frame or substrate, wire-bonded to a lead terminal of the lead frame or a terminal of the substrate by metal wire, and then sealed by resin. A DC/DC converter is then formed by externally attaching an inverter, capacitor, or the like separately to the power supply IC.
FIG. 7 is a sectional view showing the main parts of a conventional DC/DC converter. This drawing shows the constitution in which a semiconductor chip 51 such as a power supply IC, an inverter 53, and a capacitor, resistance, and so on, not shown in the drawing, are mounted on a printed circuit board 61.
The semiconductor chip 51 is adhered fixedly onto a supporting conductive plate 54 via Ag paste 56, whereupon a terminal electrode 51 of the semiconductor chip 54 and an external lead-out terminal 55 are connected by a metal wire 58. Sealing is then performed using a resin mold 59, and thus a power supply IC is formed. The supporting conductive plate 54 of the power supply IC and the rear surface of the external lead-out terminal 55 are adhered fixedly to a conductive pattern 62 of a printed circuit board 61 by solder 63, and terminals 53a of the inductor 53 are also adhered fixedly to the conductive pattern 62 of the printed circuit board 61 by the solder 63. In addition, the capacitor and resistance, not shown in the drawing, are adhered fixedly to the conductive pattern 62 of the printed circuit board 61. The inductor 53 is a laminated inductor or a flat-type inductor such as a spirally wound inductor, a solenoid inductor, or a toroidal inductor.
In this DC/DC converter, the semiconductor chip 51 serving as the power supply IC chip and the inductor 53 are provided alongside each other on the printed circuit board 61. Therefore, although the thickness is reduced, the occupied surface area increases. Hence, it is necessary to reduce the size (occupied surface area) of the DC/DC converter while keeping its thickness low when the DC/DC converter is to be installed in a portable electronic instrument.
A similar reduction in size is also required in a multi-function system LSI. In a system LSI, a large number of functions are concentrated on a single chip, leading to increase in the surface area and size of the semiconductor chip. In response to this problem, it has been reported that a size reduction can be achieved in a system LSI by laminating together a plurality of LSI chips and sealing them with resin.
This technique is known as chip on chip, in which a small semiconductor chip is laminated onto a semiconductor chip. A pad electrode for connection to a lead and a first pad electrode for an internal interface are provided on the main surface of a large LSI chip, and a second pad electrode and a first pad electrode of a small LSI chip provided on the main surface are electrically connected by a wire. Thus, a part of the circuit required by the system LSI is mounted on the small LSI chip rather than the large LSI chip, and hence a desired function as a system LSI is realized using two LSI chips (for example, Japanese Unexamined Patent Application Publication No. 2004-7017).
Further, an ultra-small power conversion device (ultra-small DC/DC converter) has been realized by flattening magnetic induction components such as a coil (inductor) and a transformer to reduce the size thereof, and improving a method of mounting these components on a semiconductor substrate in which a semiconductor device is formed (for example, Japanese Unexamined Patent Application Publication No. H11-251157).
An ultra-small power conversion device (ultra-small DC/DC converter) in which a thin film inductor of a toroidal endless solenoid is laminated onto a laminated ceramic capacitor and a semiconductor chip is adhered fixedly thereon using a stud bump has also been reported (for example, Japanese Unexamined Patent Application Publication No. 2004-72815).
In relation to the portable electronic instruments mentioned above, demands have been made for further reductions in size, thickness, and cost. Hence, there is strong demand for reductions in size, thickness, and cost of components such as the power supply IC chip and inductor built into the instrument and the printed circuit board on which these components are mounted.
Further, Japanese Unexamined Patent Application Publication No. 2004-7017 relates to a structure in which a semiconductor chip is laminated on a semiconductor chip, but does not deal with a structure in which an inductor and a semiconductor chip are laminated together.
In Japanese Unexamined Patent Application Publication No. H11-251157 and Japanese Unexamined Patent Application Publication 2004-72815, a semiconductor chip and a thin inductor are adhered fixedly by a stud bump and thereby laminated together. Although the surface area is reduced in comparison with that of the structure shown in FIG. 7 through lamination, the thickness increases.
Further, to adhere the stud bump formed on the outer peripheral portion of the semiconductor chip and a terminal electrode formed on the outer peripheral portion of the inductor together fixedly, the sizes of the semiconductor chip and inductor must be aligned such that even when a semiconductor chip having a small active region is characteristically sufficient, for example, a large semiconductor chip must be provided in accordance with the size of the inductor, and therefore it is difficult to achieve cost reductions. Furthermore, the formation process of the stud bump is complicated, and therefore, manufacturing costs are high.
An object of the present invention is to solve the problems described above by providing a semiconductor device with an inductor having reduced size, thickness, and cost.
Further objects and advantages of the invention will be apparent from the following description of the invention.